Starch residues on grinding stones in private collections: a study of morahs from the tropical rainforests of NE Queensland

Morahs are incised grinding stones from the tropical rainforests of Far North Queensland. They are made from grey slate, are roughly ovate to rectangular in shape, and have distinctive incised parallel grooves running transversely across the body of the stone. The region in which they are found is also known for the processing of toxic starchy plants by Aborigines. The process involves a relatively complex processing schedule, including cooking, pounding and leaching before consumption. Ethnographic studies have documented the processing of a number of rainforest species with starchy kernels in which morahs may have been used for pounding these kernels before leaching. A selection of morahs from private collections were analysed to determine their potential for starch residue studies. The results show that incised grooves act as residue traps for starch. In some cases the starch recovered from these grindstones enabled starch identifications of economically important endemic rainforest species, particularly Beilschmiedia bancroftii (Yellow walnut) and Endiandra insignis (Hairy Walnut). The uneven surface created by the incised grooves may facilitate the breakup of the starchy kernels, and this proposal is supported by use-wear studies on similar artefacts where soft plant processing is indicated.